MGC nodes and MGW nodes are network elements belonging to different layers of a communication network having a layered network architecture. In accordance with the layered network architecture, network functionality and network nodes are arranged in layers according to their specific areas of use. With regard to wireless and Internet Protocol (IP) Multimedia Subsystem (IMS) networks, layered networks are also known as networks having a softswitch architecture. With regard to wireline networks, layered networks are known as Next Generation Networks (NGN).
FIG. 1 shows a block diagram illustrating a layered network LN which is enabling communication between access networks and interworking networks. The access networks comprise a Base Station Subsystem (BSS), a Universal Mobile Communications System (UMTS) Terrestrial Radio Access Network (UTRAN), a Primary Rate Access (PRA), a Basic Rate Access (BRA), and a Plain Old Telephone Service (POTS). The interworking networks comprise the Internet, an Intranet, an IMS, an Integrated Services Digital Network (ISDN), a Public Switched Telephone Network (PSTN), and a Public Land Mobile Network (PLMN).
Layered network LN comprises a Network Control Layer and a Connectivity Layer. A plurality of MGC nodes belong to the Network Control Layer. MGC nodes are also known as softswitches or call agents. In case the layered network LN is a 3rd Generation Partnership Project (3GPP) circuit switched core network, the MGC nodes are Mobile Switching Center (MSC) servers. The MGC nodes are responsible for controlling mobility management, the setup and release of calls and sessions requested by end users, circuit-mode supplementary services, security, and similar functions. The MGC nodes further handle traffic control, access and core network signaling, subscriber service handling, and collecting of call charging data in Call Data Records (CDR).
A plurality of MGW nodes constituting a transport network belong to the Connectivity Layer. Within the Connectivity Layer, transportation of any type of information, i.e., user plane data, is provided via voice, data and multimedia streams.
The MGC nodes and the MGW nodes, i.e., the Network Control layer and the Connectivity Layer, may be physically separated from each other. The MGC nodes and the MGW nodes are connected via signaling links. The signaling links may be Time Division Multiplex (TDM), Asynchronous Transfer Mode (ATM), and/or IP signaling links. A plurality of signaling transfer points, IP routers, and/or cable connections may be provided within the signaling links. The MGC nodes control the MGW nodes based on Gateway Control Protocol (GCP) signaling via the signaling links.
For 3GPP standardized networks, the protocol used for the interface between MGC nodes and MGW nodes is based on the H.248 protocol specified by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). The interface is described in document 3GPP TS 29.232 V8.7.0 “3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Media Gateway Controller (MGC); Media Gateway (MGW) Interface; Stage 3, Release 8”. Furthermore, the protocol used for the Media Gateway Controller Function (MGCF)—IM Media Gateway (IM-MGW) interface is described in document 3GPP TS 29.332 V8.6.0 “3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Media Gateway Control Function (MGCF)—IM Media Gateway; Mn Interface; (Release 8)”.
Determining an exact charging time for a call is critical for the end user and for cooperating network operators which are charging calls to one another. A charging time of a call associated with a connection established via a MGW node is usually determined based on call related information written into a CDR. For this, the MGC node controlling the MGW node via which the connection is established writes information regarding the start time and the end time of the call (or a duration of the call) into the CDR. Based on this CDR data, the call time is charged to the end user or a network operator.
However, due to the separation between the MGC nodes and the MGW nodes in different network layers, i.e., the separation of call control and bearer control, over-charging of calls may happen in case a loss of communication between an MGC node and an MGW node occurs.
A first call overcharging example in case of a loss of communication between an MGC node and an MGW node is now explained with reference to FIG. 2A. FIG. 2A shows a time diagram of a call that is associated with a connection established via an MGW node being controlled by an MGC node.
At an initial point of time t1, the start time of the call is written by the MGC node in the CDR for the call. At a point of time t2, a loss of communication between the MGC node and the MGW node occurs. The reason for the loss of communication is a failure in the MGW node causing a restart of the MGW node. During the restart, all bearer connections of the MGW node including the bearer connection underlying the call are released. Thus, from the point of view of the end user, the call ends at point of time t2.
At point of time t3, the communication between the MGC node and the MGW node is re-established and the MGW node requests with a GCP ServiceChangeRequest command sent to the MGC node a change of service due to a restart. Accordingly, in the period of time from t2 to t3, communication between the MGC node and the MGC node is interrupted.
In networks having a layered network architecture, if a loss of communication between an MGC node and an MGW node occurs, the MGC node considers the MGW node to be operational until the connection between the MGC node and the MGW node is re-established, i.e., until the MGW node reports its status with a GCP message to the MGC node. At the point of time t3, the MGC node is informed by the MGW node that the MGW node has released all bearer connections during its restart. Thus, at the point of time t3, the MGC node releases the call and writes the release time t3 into the CDR. Accordingly, when determining the charging time of the call based on the CDR data, the actual duration of the call from t1 to t2 is overcharged by the period of time from t2 to t3.
In the following, a second call overcharging example is explained with reference to FIG. 2B. The example of FIG. 2B is identical to the example of FIG. 2A except that at a point of time tn, the call is released by the end user or the network. In this case, the call release time tn is written into the CDR. Thus, the actual duration of the call from t1 and t2 is overcharged by the period of time from t2 to tn.
In order to provide more exact call charging, a real-time charging mechanism is known. This real-time charging mechanism is described in document “Realizing realtime charging” by Jaco Fourie, Ericsson Review No. 3, 2006. For real-time charging, not the entire chargeable duration is measured in one piece, but the MGC node measures the call duration in relatively small consecutive time segments. However, if real-time charging is employed, the above explained overcharging still occurs during the last segment of the call.
Document EP 1 521 391 A1 describes a method for charging calls in a communication network. To avoid overcharging, a polling mechanism is proposed during which the MGC node requests from the MGW node information on which connections are still active. However, polling is not possible in case the communication between the MGC node and the MGW node has been lost.